Toxicology results released on Thursday determined that Whitney Houston had cocaine in her system when she drowned in the bathtub of her Beverly Hilton hotel room February 11. The news is sad, but it doesn't come as much of a surprise. The question many are asking themselves now is: Why couldn't Houston get clean?

In a 2009 interview with Oprah Winfrey, the Grammy-winning singer gave an honest account of her drug use, which she said started off as recreational before she began shooting the 1992 blockbuster "The Bodyguard" with Kevin Costner. But after, Houston admitted, "I had Krissy [her daughter], it started getting heavy." Her drugs of choice? Cocaine and marijuana. By 1996, she added, doing drugs "was an everyday thing … I wasn't happy by that point in time. I was losing myself."

And the public was losing its patience with her. Houston was routinely showing up hours late for interviews, photo shoots, and rehearsals. Then, in 2000, airport security officers in Hawaii claimed they found a half-ounce of marijuana in Houston's bag, but she and then-husband Bobby Brown hopped aboard their plane home before police arrived (the two were never charged). In March of that year, her performance at the Academy Awards was canceled when the "I Will Always Love You" singer was reportedly "totally out of it" during her rehearsal and kept singing a different song other than the one she was supposed to perform.

By 2001, Houston's problems took on a physical manifestation. Her skeletal frame at the 30th anniversary special for Michael Jackson that August was particularly alarming (her rep blamed family stress for killing her appetite). The public once again cringed in 2002 during the singer's interview with Diane Sawyer. When the journalist pressed Houston about her rumored drug use, she infamously declared, "Crack is wack. Crack is cheap. I make too much money to ever smoke crack. Let's get that straight. Okay?"

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Houston in 1999. (Mirrorpix/Courtesy Everett Collection)

Chatting with Winfrey seven years later, Houston — who claimed to be clean at the time — got real about her history of drug use, and it was a no-holds-barred conversation. She admitted she abused drugs because she was "trying to hide pain" from the intense pressure of being in the spotlight, as well as her tumultuous marriage to Brown. Houston matter-of-factly detailed their descent together. "We were lacing our marijuana with base," she told Winfrey. "We weren't on crack. We weren't on no crack stuff. We weren't buying $20 jumbos. We were paying money. We were buying kilos and ounces and ounces. We would have our stash."

It wasn't until Houston found the strength to leave Brown that she was able to get clean, she told Winfrey. But although she filed for divorce in 2007, her demons were still lurking. "Don't think I don't have desires for it," she said in the 2009 interview. "There are times it takes a minute to cleanse, get off. Get off me. Just leave me alone. Get off me. I have to pray it away." Houston did admit to still enjoying a drink from time to time, but as far as drugs went, "No weed. No coke. No."

Sadly, her temptations clearly got the best of her. The coroner's report on Houston revealed that in addition to cocaine, she also had marijuana in her system. "We are saddened to learn of the toxicology results," her heartbroken family said in a statement Thursday, adding, "we are glad to now have closure."